1. APOMIXSIS AND
CYTOGENETICS
Submitted by- Submitted to-
Suneel Kumar Gautam Prof. P. K. Gupta
Msc.(Ag) GPB 1st Sem Emeritus Professor
Department of Genetics and Plant Breeding
CH. CHARAN SINGH UNIVERSITY
Meerut - 250004, INDIA
2. APOMIXIS
• Apomixis includes vegetative reproduction
also.( Stebbins 1950)
• Apomixis means modes of asexual
reproduction, in which no fusion of male
and female gametes is involved, Although
the structures involved are those
concerned in sexual reproduction.
3.
4. CLASSIFICATION
Apomixis is classify in two major
classes :
(1) Sporophytic - Sporophytic apomixis
involves the direct formation of an embryo
from a somatic cell in the ovule. Like
Integument or Nucellar cells
5. .
(2) Gametophytic - In gametophytic
apomixis the embryo sac is obtained via
apospory and diplospory. In both cases,
the unreduced egg cell develops
parthenogenetically into an embryo.
Gemetophytic apomixis is further divided
into two parts:
a)Apospory- The aposporous initial cells
(AI) near the megaspore mother cells form
an unreduced embryo sac undergoes
three rounds of mitosis and eventually
develop into embryos.
6. .
b) Diplospory - The megaspore mother
cells undergo mitosis to form unreduced
embryo sac, and the apomictic initiation
cells originate from the location of the
megaspore mother cells and eventually
develop into embryos ( meiosis is absent )
7.
8. Detection of Apomixis
There are several criteria , which can be used
as identification of apomixis . These criteria
only suggest the presence of apomixis ,
which may later be confirmed by a
combination of cytological, genetic and
progeny test.
The criteria are following:
a) Failure to obtain F1 plants from a cross
(using possible apomict as female) or
production of uniform progeny in F2
population is indicator of apomixis in female
parent .
9. .
b) Uniform progeny from a Heterozygous
plant or from an open pollinated species is
the best indicator of obligate apomixis .
c) Production of maternal phenotype in the
progeny from crosses may indicate the
apomixis .
d) If plant tested for apomixis are pollinated
by a male pollinator carrying a dominant
marker , which is absent in the suspected
apomict, production of maternal phenotype
with recessive genes.
10. .
e) High seed set or uniform progeny in plant
with irregular chromosome no. Or meiotic
behaviour may also indicate apomixis .
f) Multiple seedlings per seed , flowers with
two or more fused ovaries , multiple
stigmas and multiple ovules per floret may
also indicate Apomixis.
g) The development of embryo is
pseudogamous or autonomous is also
indicate the an apomict
11. Cytology of apomicts
Association of apomixis with aberrant
meiosis and polyploidy - It has been
shown that apomixis is often associated
with aberrant meiosis and polyploidy so
that if a polyploid shows aberrant meiosis ,
there is some possibilities of the
occurrence of apomixis.
Disturbances of meiosis have been
observed during megasporogenesis in the
ovules and microsporogenesis in the
anther.
12. .
The most meiotic abnormality observed in
the Hieracium , Taraxacum, Antennaria
genera are -
1. Failure of chromosome pairing .
2. Failure of contraction of chromosome .
3. Retardation of meiosis .
4. Precocity of meiotic division .
5. Multivalent formation.
These abnormalities were attributed to
hybrid origin of these apomicts.
13. Megasporogenesis and
megagametogenesis in apomictic plans
• In apospory megasporogenesis is disrupted
and the sexual tissue abort before functional
megaspore formation or embryo sac
development. Example. Some grasses poa ,
paspalum
• A nucellar cell enlarges and become
meristematic , its nucleus divides mitotically
twice giving a 4 nucleate unipolar embryosac
with an egg cell ,2 synergids and a polar
nuclei (but no antipodal cells).
14.
15. .
• In diplospory is more difficult to identify
cytologically , in this case megaspore
mother cells enlarges and forms
megaspore directly without meiosis .
• Rarely the meiotic division is followed by
formation of restitution nucleus, to form a
dyed of 2 unreduced megaspores one of
them forming a 2-8 nucleate embryo sac
with an unreduced chromosome number.
16. Apomixis in some species
• Dichanthium- Bothriochloa- Capillipedium
• Poa
• Potentilla
• Blumea
• Crepsis
17. Apomixis in Plant Breeding
• The most obvious advantage of apomixis
is that it can be used to fix hybrid vigour to
produce to breeding hybrids.
• This would have the greatest impact in
crops where hybrids are more productive
but male sterility or fertility restoration
system are not known .
18. .
• This will also be useful where production
of hybrid seed is so expensive , that the
higher yields realized from the hybrids
does not compensate well for higher price
of the hybrid seed .
19. CYTOGENETICS
• The relationship of specific genes with
specific chromosome is actually the science
of cytogenetics.
• In other words, Cytogenetics is correlated
study of genetics and cytology .
• Cytogenetics is essentially a branch
of genetics, but it is also a part of cell
biology/cytology , that is concerned with how
the chromosomes relate to cell behaviour,
particularly to their behaviour
during mitosis and meiosis.
20. Techniques in Cytogenetics
• Techniques used include karyotyping,
analysis of G-banded chromosomes, other
cytogenetic banding techniques, as well
as molecular cytogenetics such
as fluorescent in situ hybridization (FISH)
and comparative genomic
hybridization (CGH).
• Gene mapping
• Study of chromosomal Aberrations
( structural and numerical both)
21. References
• P.K Gupta : Cytogenetics: An Advanced Study
Rastogi Publications , Meerut
• The steps from sexual reproduction to apomixis
Xitong Fei, Jingwei Shi, Yulin Liu, Jinshuang
Niu &
Anzhi Wei Published: 08 April 2019
• Google Also .
